Quadratic Equation Solver - Revisited

Problem Statement

if b*b-4*a*c is non-negative, the roots of the equation can be solved
with the following formulae:

Write a program to read in the coefficients a, b and c,
and solve the equation. Note that a quadratic equation has repeated
root if b*b-4.0*a*c is equal to zero.

However, if a is zero, the equation becomes a linear one whose
only solution is -c/b if b is not zero. Otherwise,
if b is zero, two cases are possible. First, if c is also
zero, any number can be a solution because all three coefficients are zero.
Otherwise, the equation c = 0 cannot have any solution.

Program Input and Output

Since we have been doing the quadratic part in several similar examples,
the following concentrates on the order part of the program.

If the input to the program consists of 0.0, 1.0 and 5.0,
we have the following output. Since a is zero, this could
be a linear equation. Since b=1.0, it
is a linear equation
1.0*x + 5.0 = 0.0 with the only root
-5.0/2.0=-5.0.